Mop-up equalizer



Aug 19 K. W. PFLEGER MOP-UP EQUALIZER 'Bv @JMW ATTORNEY Aug. 19, 1952 K.w. PFLEGER 2,607,851

MOP-UP EQUALIZER Filed Nov. 18, 1947 7 Sheets-Sheet 2 RECEIVING STAT/0NFEED L ATTEm/A r/o/v sol/A1. /zER (F/c,5) (F/G.5)

THERM/srok HEATERs g3 CONTROL CONTROL CIRCUITS CIRCUITS FOR DELA Y FORLOSS EQUAL/2ER ADJUSTER (F/GJ) (ff/6,4)

N PHASE/wo L EVEL ADJ.

BAND PASS F/L T ATTORNEY Aug. 19, 1952 K. w. PFLEGER MOP-UP EQUALIZER' 7sheets-sheet 4 Filed Nov. 18, 1947 RESUL TANT ODD HALF gew-0F 4 /XEDHUMP FREQUENCY ATTORNEY Aug. 19, 1952 Filed NOV. 18, 1947 K. W. PFLEGERMOP-UP EQUALIZER 7 sheets-sheet e A 7` TORNE Y llg- 19, 1952 K. w.PFLl-:Gr-:R

MOP-UP EQUALIZER 7 sheets-smet 7 Filed NOV. 18, 1947 a mop-up equalizerin accordance with the invention;

Fig. 2 is a schematic block diagram of receiving end apparatus adaptedto be utilized with the sending end equipment shown in Fig. 1;

Fig. 3 is a circuit diagram of one of the manual level and phaseadjusters forming part of the equipment shown in Fig. 1 and Fig. 2;

Fig. 4 is a circuit diagram of one of the control circuits forming partof the arrangement of Fig. 2;

Fig. 5 is a circuit diagram of a group of typical distortion equilizerssuitable for useV in the arrangement of Fig. 2; i

Fig. 6 is a graphical representation to aid in understanding theinvention;

Fig. 7 is a schematic block diagram of control circuits which can beutilized in the arrangement of Fig. 2;

Fig. 8 is a circuit diagram of a phase detector which can be used in thecontrol circuits of Fig. 7;

Fig. 9 is a schematic circuit diagram of a switching arrangement formaking unnecessary a considerable amount of the receiving end apparatusshown in Fig. 2;

Fig. 10 is a schematic 'blockdiagram of an attenuation equalizer whichproduces practically no delay distortion;

Fig. 11 is a graphical representation to aid in understanding theoperation of the arrangement of Fig. .10; and

Fig. 12 is a circuit diagram illustrating how the, switching arrangementof Fig. 9 is connected into the receiving circuit of Fig. 2.

Y Referring more specifically to the drawings, Figs. 1 and 2 show, inblock diagram form for purposes of illustrating the invention, sendingand receiving end portions I0 and II, respectively, of a televisionsystem in which mop-up equalization of loss and envelope delay areemployed. For simplicity in the drawings, details of the equipment forgenerating, transmitting and utilizing the video signal at the receivingstation to produce an image of the object have not been shownsince thepresent invention is concerned primarily with the loss and delayequalization of the television signals.

Referring first to the sending end equipment I0 shown in Fig. l, astandard frequency oscillator I2 generates oscillations of, for example,1000 cycles per second, and this generated wave is applied through ahybridcoil I3 to a multivibrator and harmonic generator I4 of anysuitable form to produce a groupof accurate frequency waves.` (Thestandard frequency wave can also be applied through the filter 30 to thesynchronizingcircuits forming part of the television sending set I5, forcontrol purposes.) By means of a multiplicity (for example there mightbe 191 for` television having 441 lines and 30 frames per second)` ofnarrow band-pass lters 20, 2l, 22, 23, 24, 25 29, 30 tuned tofrequencies separated bya frequency of 13.23 kilocycles (the linescanning frequency), a multiplicity of frequencies are selected asfollows:l Fc (carrier frequency-for example, 300 kilocycles per second),Fc-F (where F is one-half line scanning fre- QUEHCY),

Where the lower sideband of the television signalis suppressed, it isnecessary to transmit relatively few pilot frequencies below Fc. Thecarrier frequency Fc is modulated in the modulator I6 with a videosignal passing the hybrid coil I3 from the television sending set I5 andthe resultant modulated wave is passed through a single sideband filterI'I and the amplier I8 to the toll line I9. The selected frequenciesFc-F up to F-{(2N-3)F are each passed through an individual one of themanually-adjusted phase and level adjusters 3l, 32, 33, 34, 35 39, 40(to compensate for any phase or level change in the filters). Suitablephase and level adjusters are shown in Fig. 3 and will be describedbelow. Each of the selected frequencies is then passed through anindividual one of the narrow band-pass filters 4I, 42, 43, 44, 45 49, 50to prevent that frequency from interacting with the phase or leveladjuster for any of the other frequencies. Then all of the selectedfrequencies are applied through the amplifier I8 to the toll line I9 andtransmitted to the receiving station I I shown in Fig. 2.

At the receiving station II of Fig. 2, all of the selected (pilot)frequencies (Fc-F to Fc-{-(2N3)F, inclusive) as well as the transmittedmodulated wave containing the video signals are passed through anamplier 5I and then through a delay distortion equalizer 52 (which willbe described more fullyrbelow in connection with Fig. 5) and anotheramplier 53. The output current of the amplifier 53 is divided into threeparts as follows: (1) a portion going through a resistance pad 54 to anoutput circuit terminal 55 to which are applied (by means to bedescribed below) the pilot frequencies to oppose those in the amplifier53 and thus leave only the transmitted modulated wave containing thevideo signal, (2) a portion going through a feedback circuit containingvariable attenuation equalizers 56, and (3) a portion going through amultiplicity of parallel circuits each comprising one of the narrowband-pass filters 6I, 62, 63, 64, 65 69, 'I0 and one of the amplifiers1I, 12, 13, 14, 'I5 19, 80. The output current from each of thelast-mentioned ampliers is then divided into three parts, (1) a portion(A) going through an individual one of the control circuits 51 for theloss adjuster (which circuits will be described more fully below inconnection with Fig. 4) which varies the current through an individualone of the thermistor heaters 8l, 82, 83, 84, 85 89, 90 in one of theattenuation equalizers of the feedback circuit 56, (2).a portion (B)going through individual phase and level adjusters 58 (which will bedescribed more fully below in connection with Fig. 3) and narrowband-pass filters 9i, 92, 93, 94, 99, |00 to the output circuit terminal55 whereby the pilot frequencies are adjusted in phase and amplitude tooppose those in the output circuit of amplifier 53, and (3) a portion(C) going to an individual one of the control circuits 59 (which will bedescribed more fully below in connection with Fig. 7) for varying ineach case the power of an individual heater for an individual impedancemember of the distortion equalizer 52 shown in Fig. 5.

Referring now to Fig. 5, this figure shows-one form of equalizer whichmay be Vused as the delay .distortion equalizer -52 or the attenuationequalizer 56. It comprises avrst section IUI consisting of amultiplicity of parallel connected branches III, II3, II5, II'I and IIS,...Bn respectively resonating at a diiierent one of the odd-numberedpilot frequencies and a thermistor, followed after resistance pad |02 bya section 5; 1.0.3 'like .the lfirst 4section |:0'I .but .tuned at theeven-numbered .pilot lfrequencies. Considering one of Isaid branches,as, for example, the-br.anch 11|, it .comprises a capacitor member |04,an inductance ,member |05, resistance member |06 and a thermistor member|01, the other parallel branches H3, H5, ||9, Bn, and also those in theeven-numbered section |03 being similar to the branch except that thefrequency of the tuned circuit varies. By varying thejresistance` of aparticular thermistor |01- by Avarying the'current in its correspondingheater 8|, .83, 85, 81, 8S, Hu, the magnitude of the hump .of lossinserted into the system at that pilot frequencyv can be varied. The re'sultant of the two sections and |03 is substantially-'flat for theovereall frequency range. .esY the .arrangement shown inFig. producesboth attenuation and delay it can be used either asa delay distortionequalizer52 or attenuation equalizer 56. v A

When the thermistors |01 are all at some average value, itis desirablethat the receiving circuit .of Fig. 2 shall have an over-allrflatcharacteristic. .Since the network of Fig. 5 produces peaks of loss (orattenuation) at each odd-numbered resonant frequency, it is necessary tohave in connection therewith a similar lcircuit |03 having` the parallelbranches thereof tuned to even-numbered pilot frequencies. At averagevalues of the thermistor, the loss hump has about the same peak values.at ally pilot frequencies and the loss characteristic due to the onenetwork is complementary to that of the other so that over-.alltransmission is flat when all the thermistors are at an average value ofresistance. The use of sinusoidal humps is advantageous. In general, foraverage values of thermstors or other possible variables, theoddnumbered network produces an over-al1 loss, for example, as shown bythe dash line curve in Fig. 6. The even-numbered network |03 gives thecomplementary loss shown by the full line curve so that the resultant isat for the frequency range of interest. By variations from the averageof one or more networks, the resultant can be made to have either narrowor broad humps depending on the changes occurring in adjacent channels.On Fig. 6, which is a plot of loss versus frequency, the loss curves forboth halves of the equalizer and the resultant have been shifted torefer'them to an arbitrary zero loss axis in order to facilitatecomparison. A curve similar to Fig. 6 can be drawn for delay versusfrequency.

' When simple networks of the vtype shown in Fig. 5 are used forlossequalizers, delay humpsf are also produced and when they are used fordelay equalizers, loss humps are also produced. Resonant shunts areshown in Fig.,5 merely to illustrate how the pilot channels can lcontrolhumps of loss lor delay. In practice, some other form of tuned networkmight be preferable.

A s an example of an attenuation .equalizer which produces practicallyno delay distortion, ref- .erence will now be made to Fig.y 10.

6 around :the tuned frequency, f-a .respective .xed delay "equalizer.1:1||,;|4.2, 143, 1144, M5, '|46 or'lr50. for compensating foranydelayin .the corresponding filter xandpsaA 'respective variable resistorelement |`5 .152; @l5-3, |54, .155, 1| 56 l. er1-6.0 (which maybethermistors) for varying the ifntensityof the .hump. The equalizer -ofFig.. V10 can Yalso beintwov sections like the one of Fig. 5, onesectionhaving the odd-numbered branches and theaother section havingthe: 'evenev numbered branches. Byirneansyof this arrangement, AAhumps.of- .correct Jamount, of. loss `can be inserted into `the system attheaprop'er Lfre'- quency to give :substantially-ilat compensation.

The characteristics fof '-the- 1nfthchannel are has a lmaximum at Fn,the-nth pilot frequency, and lis'gpreferably negligible at and-beyondfrequency Fn+i and Fn-i respectively'corresponding to the .pilotYchannels v11f|1 lor ,na-1. 'The delay of the lter` alone has ,h-uanpslas shown .by the dash line curve of Fig. ill.l It :is for thisreasonthat delay equalizers areV included ingeachchannel of the .arrangementof Fig.; :1,0 to make the delay constant over the transmittedfrequencyrange of vthe channel. Thetotaldelay is .the same' for each :channel .infits; transmitted 'frequency range. The resistance3(|5| |60) in theoutput of each of the :parallel lconnected branchesof the circuito1E.Fig.'10` can be varied. It is 'assumed that all .imp edances asseenfrom the resistances |"5| .'f|60havezbeen adjusted to have zeroangle which can bedone by using constant K-type networks. Thereforethese Aresistances |5| to |60 control the relative outputs of thechannels without altering the delayor the shape of the amplitude versusfrequency characteristics. When the resistances` are set so that eachchannel transmits the same current magnitude at its mid-band frequency,and when `the amplitude versus frequencyy characteristic of eachVchannel above 4its mid-band frequency is complementary to that ofrthenext higher channel below its mid-band frequency, then the overalltransmission versus frequency:characteristic |30 each consisting of arespective band-passV for the entire .circuit of vrlirigl() will be fiatfrom F1 to the mid-bandv frequency of, the highest channel. Gain or.`loss vhumps `can next be inserted at will by varying the adjustableresistors|5| to |60 withno effect on the delay since all channelshavevthe same constant delay.v Where the number .of channels in.parallel is great there will be considerable loss due to the shuntingeffects of so many branches at each junction point. This may be reducedif necessary by the use ofl amplification and the subdivision ofchannels into groups, each with a separate amplifier if necessary. Theresistors |5| to |60 can be thermistors operated by heaters similar tothose in Fig. 5, if desired.'

A combination of an equalizer of Fig. 10 with an equalizer. whichproduces both delay and attenuation effects or delay effects onlypermits compensation of any desired delay or :attenuation distortions,either separately-or together. j

In the circuit of Fig. 2,`the\delaydistortion equalizer 52 (such asthatshown in Fig. 5 or Fig. l0) is shown at the input to theamplier 53in order' to prevent unfavorablephase relations from arising in thefeedback circuit including the attenuation equalizer 56. VIt isintendedthat small incidental` loss variations caused by the delay network beautomatically Acompensated by the attenuation equalizer and incidental`delay variationsof the `latter, if not Ytoo great be compensatedforbythedelay equalizers. By providing practically instantaneous controlsusing fastacting therlnistorsx in1the variable networks, the two typesof compensation can be made to cooperate simultaneously in producingover-all flat loss and delay Versus frequency characteristics.

lEach of the control circuits 51 in branch A of the circuit of Fig. 2can be of any suitable form. An example of one satisfactory circuit isshown in Fig.' 4. In the arrangement of Fig. 4, each pilot frequency isapplied to a rectifierV |6| through'a'high frequency attenuator |52having constant impedance. The output of the rectifier appearing acrossthe resistor |63 is applied to any convenientform of oscillator |54 tocontrol the variable output to heat'anyA one of the thermistors 8|, 82,83 90. vThe connections inFig. 4 should be poled so that a suddenincrease in level of apilot channel on the' line causes thecorresponding thermistor resistance to vary in a direction to increasethe amount of negative feedback (through the attenuation equalizer 56)permitted at this frequency, until the level of the pilot frequency atthe amplifier output is reduced to the former value. y A similarprocedure follows with opposite signs when the pilot level decreases.

`The branch B of circuit shown in Fig. 2 includes a multiplicity ofphase and level adjusters 58. A suitable manual 'level and phaseadjuster is shown in Fig. 3.V This comprises a high frequencyattenuato'r |66, a 4shunt-connected. inductance member |61 andvariablecapacitor member |08. The capacity |68 can be varied to producethe level and phase adjustment desired.

Reference will now be made to Fig. 7 which is a single line schematicdiagram of a control circuit suitable for use in the lpath C of thecircuit shown in Fig. 2, or, in other words, it can be used as thecontrol circuit 59 of Fig. 2. Before describing the circuit arrangementof Fig. '1 it seems best to describe its function. Suppose the circuithas beenvlined up initially to have zero delay distortion. Suddenly thephases of the N pilot'channels are shifted respectively byincrements/8i, 132, s, etc. where vthe subscript in each case denotesthe number of the channel'. It is assumed'satisfactory if the automaticdelay distortion`c`ompen'satorso operates that cies, this keeps A/Awa'constant over the entire A Aw to represent .delay instead of @E da 8to -z-r In order-'to provide a test for z-i, s-2,'4-3, etc. the N pilotchannels are connected to N-l demodulators as in the arrangement of Fig.7. These demodulators are designated by the reference characters |1|,|12, |13,

|14, |15, |13, |11 |19, |80. At the outputs of the demodulators arelow-pass filters IBI, |82, |83, |84, |85, |86, |81 |80, |90, and at theoutputs of all of these filters the difference frequency, 2F, appears.In each channel, the phase shift is respectively equal (Within aconstant) to [i2-[31, s-a ,S4-ps, etc. In order to test these phaseincrements f or equality they are compared to some standard, forexample, to [347-53 appearing at the output of low-pass filter |83, orin similar' fashion, any other filter output can be selected. Anaccurate means of detecting phase shift is the 90-degree, push-pulldetector shown in Fig. 8. A phase detector such as that shown in Fig. 8is sensitive to .01 degree even when level changes occur in the twoinputs of magnitude about one-half decibel. For the frequency interval2F=13,230 cycles, the envelope delay sensitivity is .0021 microsecond.In order to compare phaser changes at the output of low-pass filter |83with phase changes in the output of the other low-pass filters, N-2phase detectors |0|, |92, |93, |94, |95, |06, 200 are arranged as shownin Fig; 7, each deriving one input from low-pass filter |83 and theother input'from some other low-pass filter (|8 |02, |80, |85,|8`8, |81or |90). In tandem with these connections are connected N -l manualphase and level adjusters 20|, 202, 203, 204, 205, 205, 201 209, 2|0 soset that when no delay distortion exists on the line, the two inputs ofeach phase detector are degrees apart, and the direct current output isthen Zero. (It is possible to omit the phase adjuster 203 if the othershave sufficient range.)

The phase detector (|92 for example) shown in Fig. 8 comprises aresistance bridge 2| across the upper and lower corners of which is.applied one wave of frequency 2F from transformer 2 I2 connected to onephase and level adjuster (20| to 2 0) of Fig. 7 and across the right andleft corners of which is applied a wave of frequency 2F from transformer2|3 connected to another one of the phase and level adjusters20| to 2|0.The upper and lower corners are connected respectively to rectifiers 2Mand 2| 5. Between the positive terminals of these rectiers is connecteda series circuit comprising resistors 2 I 6 and 2 1 the common terminal2|8 of which is connected to the right-hand corner of the bridge 2| l.Serially connected resistors 2|6 and 2 I1 are shunted by a condenser2|9. The operation of circuits like that shown in Fig. 8 is well knownand will only be given a brief description here.

The current in the upper right arm of the bridge 2|| is the vector sumof the two sinusoidal waves from sources 202 and 203, and the current inthev lower right arm of the bridge 2|| is the vector difference of thesewaves. When the magnitudes of the twoinputs are equal, the vector summay be expressed by ES=2A cos g and the vector difference by ED: 2A sinl9 vby some suitable network.

v 9j values Esfand- En. asaretli'e: rectlledwaves-flow--y inginresistors 2l'6'and"2IT.l A'Io'wepass filter consisting of shunt:condenser 25|?!E and' series inductance 222 removes alternatingYcomponents:

from the output wave flowing Vover conductors- 22 i Due to thedifferential combinationrof thevoltagesacross 216 andf2/I1f theopencircuit-output voltage across conductor. 22| is prcportio'nalto(nel) plus the voltage-ofiarbiasingzbattery 221e; When :90" and athermistor .heater or; loadiis, con,- nected to leads.A 22| .thecurrentflowingztherein.is

due entirely tothe; voltage .iotvbattery 22S;- But:

if the'. twov inputrvolages'fare not dn -S'Oedegrele ,-r ev lationship,therloact currentgissinrreasedaor des creased byan.arnountiproportionaittouv a direct current component inthe output-'from4 For 'eXampleL suppose it, isec'le Mred tor increasea-zarneseffhunflr:Similarie.shape to the attenuation ffnumpf! inf-rug'.-e withr a peak. i at Fc-1-3Ffshown by the dashedcurveicanbe ir'iserted'A In-'termsot envelope deler.:

thisjl` phase characteristiel would havea delay hump A`at about Feel-2F@It' v'islthusievident'- that thcvarious phase detectors-i i194 -to' -2'00)* are to control del'ay l"humps havingk peak valuesabout inidv'waybetween `the"associatedy pilot frequencies. Fig'.` 6y can be 'assumedto'applytofdesirabledelay equalizers-v at average conditionsl ifl thehumps are taken to'den'otel phase shift instead of loss.

tlis' obvioussthat as the'device of this sort makes rela-tivelphases ofthe power channel should be definitelyadjust'ed at the sending '.endinsuch a maneras not to causer serious resultant peak values onAthe-line.; The-*sending arrangmentsshould be stable sor-that this phaserelationship remains fixed? Within about' i101- 'degreeinr each case inlorden-not to produce# appreciable subseinterchang'eable. The'` receivingarrangement ofi Fig. f 2 connected" to 4the''sendirig arrangement ofFig. l through zero 'lineV and. the:V pilot channels and manualadjustments ofi the reeeivirgare rangement are set so thatcomplementary'parts of the delay and loss adi-listers:givefover-allfiat.-characteristics. Itis. also-important `for certainll parts of thereceiving-Lcircuit-to be kept' at constant temperature and to beas-stable asthe send-ling circuits. After adjusting-.a receivingcircuitv it can be; removed to its-fnalldestination.- vllaelti sectionof. circuit to.A be controlled bythe automatic device isfirs't givenasiiataniadrjustment of lossand delay as possible with' the basicequalizer'svv cf the system before the automatic device 'l is.: added.Consequently, straightawayl loss and -delay distortion measurements aredesired. The narrow band-.pass filters which separate lthepilot channelsfrom` `the television current should! have high impedance to preventunfavorable sli-unt lossand delay of the through transmission.-

It is obvious thatthe amount of apparatu'sfor one sendingancl onereceiving circuit as shownini Figs. 1 andV 2 is considerable. It'vis'-given/below in the table in the column-headed-Casel.- This4 table alsogives two other' cases, Case II' andCase- III' which will beexplainedhereinafter.

If. the carrier isl an; odd multiple. offhalfthe4` line speed, forexample V2957.??? kiloc'ycles.- and 'if Athe multivibrator Id'give'sonlyh'armoni'cs of the line speed., they allfall .inthecentersl oflth'edead bands. In this caseina'irow'bandpass--lters are not needed` in. thesending circuit-of 'eachvpowerl channel, but an additional multivibratormaybe necessary as-the carrier may have tbibe generatedseparately.Theamplitudelandphasesof all-the pilot channels can?beladustedv by`asinglel wide` band equalizer.` theAreceiving-circuit"of-Fig.l2,- the N`stable ampliersi H` I` te 18W inclusive caribe. omitted/if the -le'velat-therpointr inFig/Z is-inade high enough. Insteadga singlewide-bandamplif-V er. canbeinserted inAv the leads toswitczh-v S'in-Fig 2. Withthese simplilcations-thelapparatuscanbe reduced to` the' `amount shownfini `tl'iecolumn headed Case II--in ther-table. However; the-har#-rnonic generatorshave to. berv madeal-l 'alilel order to beinterchanegable. Also, the ZOSZiPk-i-lo# cycle pilo-tfrequency of thebasic equalizersr.haof` tobe shiftedrto' avoidconilictlwitli-thetelevision signals. If inl a'V particular system litturns-iout thattheattenuation equalizers E'kcanbe made to` take care f ofdelaylequalizaltion without ltli'e V need of separate controls forpha'sei shift; further re duction in apparatus-.canbemadelto the? amount showninthe coliimrrheadedCaselinthetable.`

Moreover. aconsiderablelamount ofexpensive y receiving end apparatus`can kbefsave'idf the: con

trolr circuit for only."onepowerohannelris used to make all adjustmentsforfa group offchanneisl but ituis thennecessary to switch?thefcontroiicircuit input. continuallyA toarthelnutputs'. ofi various receiving.pilot channelfilters'n inL/thisl. group,v while switching; the control?circuits? outs` put or outputsto 4therespective. variables. elef#mentsof `the associatedtunedY networks.. Withthis arrangement`instantaneous?. controlT isfsa'cri-H- ced Ain favor. ofy cheapnessg'.yand nautomaticSade justments f on: each channel are; made'at. fregularintervals orperhaps' every-few. minutes;

A switching circuit makingiuse or? .thexcha afi.

into the receivingcircuit ofFlg. Z'iisshown int Fig. 12.' In thisarrangementfalgroupict' Npil'ot' channels controls-:an attenuationadjuster'. nd

a delay adjuster-covering?'ai'wide rangez-:ofiz're'a quencies, usingonerectiler andonezpha'eeizdeY tector. ,"The circuit arrangement shownin Fig, 9 represents the m'th switching circuit, of which a total ofv Nis required. Aldistributor 239 having NV segments (m-l, 1mm-H etc.) isdriven by a motor (not shown) and direct current flows from source 232through the b-rush 23| and the mth segment to operateswitching circuitsassociated with eachsegment.' The magnets M1 and Mz for them'thswitching circuit (for example, the switching panel designated S. P. No,2 in Fig. 9) are then energized to close their contacts which; arerespectively associated with trunks 29,3and 29.4.

Y Trunks 29,3 and 294 are here shown as two wires but, on' Fig. 12 areshown as one wire as `the latter gure is a single line diagram showinghow the N pilot frequencies of Fig. 2 after leaving amplifiers 1|, 1213.80 are trunked to the various switching panels. AThus trunks 29| and2,92` goto the first switching panel (S. P. No. l), trunks 293 and 294go to the second switching panel' (S. P. No.' 2), etc. Fig. 12 showsthat two pilot frequencies, for example, F|3F and Fc|5F are applied'tothe demodulator |13. The frequency 2F is obtained at the demodulatoroutput, is passed.v through low-pass filter |83 to remove highfrequenciesV and through phase and level adjuster 203, these membersbeing similar to apparatus shown in Figs. 3 and '7. This frequency 2F ispermanently applied to the phase detector 210 shown in Fig. 9. lThephase and level adjuster 2,93 is set sothat when switching circuit No. 3is connected to trunks 295 and 296 of Fig. 12, the, two currentsentering the phase detector 210 of Fig. 9 are 90 degrees out of phasefor ank average loss and delay adjustment. The other phase andl leveladjusters of Fig. 12 (28|, 282, 285, 289, 23|)A whichcan be of the formshown in Fig. 3) operate Vat line frequencies and are also set to givethe vEJO-degree relationship between the two inputs oftheA phasedetector of Fig. 9 when an average loss and delay adjustment is desired.The lines carryingthe pilots FQ-l-SF and Fc-l-F need no phase andileveladjusters in this position ,because a phase andlevel adjuster 293 isprovided. l

The same magnets M1 and M2 which connect the switching circuit to a pairof pilot frequency channels also operate clutch 235 (and a similar oneinthe apparatus for'operating potentiometer No. 2 shown as a box inthearrangement of Fig.

9). It will be understood that potentiometer No. 2 is similar topotentiometer No. 1 shown (within dashed lines) immediately above it.The operation of the clutch 235 closes .a mechanical circuit whichpermits motor No. 1v (element 236 in the drawing) to turnthepotentiometer No. l (element shown within the dash line box 253inthedrawing) and the operationv ofthe clutch in potentiometer No. 2 (theelement shown within the box 254) causes motor No. 2 (element 231) toturn therotating element in potentiometerV No. 2. Potentiometer No.1comprises a rotating shaft 238 which drives a crank 239 having a brush240 on one end thereof which is drivenacross commutator segments 24|,242,243, 244, 245,246,

This causes one ormore resistors 252 Yand clutch 235 to ground ontheframe 233 sup-x1 porting the clutch handle 234. Potentiometery No.2'variesgthe current Vthrough heater 26|),which is fed by current fromthesource 26| inA thesame manner. The motor 236and the motor 231'operateas follows: f 1

The m'th and. (M +1)st pilot frequenciesiafter having been received,filtered and adjusted at the level and phase adjusters 28| to 290 appearon trunks m and mel-,1 respectively. Operation of the relays M1 and M2applies the waves of these frequencies toY demodulator 262 and one ofthem to the rectifier 263. The output of the rectifier 263 causesfapolarfrelay264 to operate,

this latter being 'biased to have :zero loperating force when theVrectifier 2631 receives average power and no contact is then made.AAny'deviation from this power causes.' the Yrelay 264 to flop to oneside or thevothenf: The bias of the relay may be provided by'anysuitable means such as, for example, the circuit including theresistance 265 in series with thesource 266 and biasing winding of therelay 264. 4The operation of the armature of the relay 264 to itsleft-hand side connects 'source 261 in acircuit startingrwith ground andwhich passes through the source 261, the armature of the relay 264,connection 268, andthe field winding of the motor 236 back to groundwhile the operation of the armature of the relay 264 to its right-handposition completes a circuit starting with ground l and passing throughthe source 269, the armature of the relay 264, connectionv 268, andmotor 236 to ground. Since the sources 261 and 269 are oppositelypolarized, the question of which source is included in the circuit withthe field winding of the motor 236 determines theV direction of rotationof this motonand theconsequent adjustment of potentiometer'No. 1v(element 253) which controls an attenuation equalizer of the type usedin equalizer 52 or 56. p

Demodulator 262 (in cooperation with the lowpass filter 21|) puts out afrequency 2F equal to the difference between the two adjacent pilotfrequen-cies and, as previously explained, any sudden phaseshift thereofcauses a shift in the difference frequency equal to the increment inphase shift between the pilot frequencies. Another demodulator similarto demodulator 262 and which is called demodulator No.1'13 is fed by anytwo adjacent pilot frequencies whose relative phase increment it isdesired to use for a standard. The direct current output of the phasedetector 210 is a measure of the inequalityV of the phase increments andtherefore of delay distortion. Phase detector 210 is the same as'the oneshown in Fig. 8 except that there is no'biasing battery (such as thebattery 220) needed. The polarrelay 21| then operates the motor 231 inadirection suitable for changing the setting of1 potentiometer No. 2(shownas box r254) until the delay inequality is compensated.V This isaccomplished by the oppositely polarized sources 212 and 213 a selectedone of which is connected in a series circuit (starting with ground andincluding the connection 214, and the eld winding of the motor 231 whichis connected to ground) when the polar relay 21| is operated to eitherits righthand or left-hand position. l

After a reasonable timel has elapsed land the adjustments are complete,motors 236and -231 stop and the br-ush 23| passes from the mth switchingcircuit (shown in Fig. 9) to the (m-|l)st switching circuit (not shownvbut which is similar to the mth switching circuit shown in Fig. 9) wherea similar process is repeated, using the (m-|-l)st and (m4-mnd pilotfrequencies to con-Y 13 trol the-same motors 286v andA 23'l'while theyoperatethe (mf-i-Dst sections ofthe. equalizers in l the boxes 552land56.

Thel effect of this switching scheme, as shown in the table below, is toeliminate about 188 demodulators, 188 phase detectors, 380- oscillatorsand 190 rectifiers, or a total of-946 active devices', adding,-hovvever,3- motors and 191 switching-cirNv cuits, in Cases I and II. In Case III;only Zmotors are; requiredv as motor No'. 2- (element '231) can beomitted. Thenet saving` is vabout '752activede vice's in Cases' I and I1and188 in Case III, as shown in the table given immediately below:

Table. [Approximate amount oi' major apparatus for, one, mop-up,equalizer, 2F=1a23 rc, N=191.]

v Case I.

C ase,.II Case/III Passiv; Networks Narrowf'Bandk Filtersr. 766 384 384Lowrass Filters,.-- 19o 19o Manual Attcnatqrs 763 5.72 382 ManuelPhaseshifters 572 381 101 l, 150 F. Switching (seqnot'e belowl... 188188 Remainder 2, 484 1, 721 1, 150 AtiveApparatlus: Y

Temperature" Controls A 2 2 2 Amplifiers 193 3 3 19o 19o 380` r380 191191 191i 191 139 189` `1 1 1 Multivibrators. l 2 2 Totals, V l, 147 95839D SavingIn/.fictive` Apparatus due to I 'Switching- (see note below).7. 562 562 188 Remainder 585 396. 202 GrandTotals (Active plusPassive): v

- Without switching.... 2, 867 1, 540 With switchinv 2,117 1, 352

Case I. -I-`igures 1 to 8' inclusive. Case ILT-Same as, Case I withlimitations incarner frequency and m flexibility of adjustment ofrelative phases and amplitudes of pilot frequencies, and reduction innumber of amplifiers,

Case, IIL-Same as Case II omitting separatey delay` equalizationNoun-Switching arrangement .per Fig. Q'except motor No. 2, magnetSMz',and potentiometerslNo; 2'are'o1nitted`for Case III. Phasegdetectors,modulators-Landlow-pass iiltersofligs. 7 and 12 are alsoomtted inv GaseIII; and thephase shifting parts of phase and lovclafijusters arealsoomitted in `Gase III.

N plotfrequencies neednot be transmitted `si multaneously if only afeWareus-ed' at, a time, andj the switching arrangement shown in Fig. 9makes possible. areduction 'in' load upon the line and, therefore,V inpossible modulation trouble, if, lin addition, selective switching. ofpilot frequencies is done at the sendingend. Synchronous switch' ingisunnecessary ifl relays are utilized to operate the receiving enddevices instead of the commutator. Relaysto be activated by pilotfrequencies might 'require some sort of detectors (these items are notincluded in the table). Switching of pilot frequencies at thecsendingend can be done at' the vinput of the, narrow band filters of Fig. 1,that is, filters-,2D to 30 and Ill to U, in order to limit lthefrequency content of transients upon the line. There are usually fourpilot frequencies simultaneously Yon the line 'in order tokeep one phasedetector busy but if separate delay adjusters are unnecessary there needbe only one pilot frequency on the line at one time. 'Ifhis.of course,does not include pilot frequenciesto. control the basic equalizers.

Various changes can be made in the variousembodiments describedl abovevwithout departing from'the spirit of the invention the scope of whichis indicated in the claims. A divisional 1. In combination, a broad bandtransmission path for television-signals-produced by scanning afieldalong elementallines in succession, means for-generating oscillationslofv a standard` frequency, means for` .deriving from saidv standardfrequency oscillations av multiplicity of harmonic frequencyoscillations'means-for selectingv from said multiplicity of oscillations anumberofpilot frequency Waves of differentifrequencies' each yone spaced froman adjacentzoneby-the line scanning frequencyand locateda portion of theband which contains inappreciable ltelevisionsi'gnaIenergy, meansrfortransmittingA said pilot frequency Waves to a receiving stationv oversaid transmission path which produces attenuation and envelope delaydistortions, means -a-t-the receiving Astation under controllofsaidpilotfrequency Wavesto producecorrecting increments of loss and envelope,delay of the proper-magnitudesv and at the r respectivev4 pilotfrequencies to. give substantiallylv fiatcompensationsof the iattenuation versuswfrequency and'lenvelope delay vthe band whichcontainsinappreci'able television` signal .energy, means 'fortransmitting said pilot frequencyiwaves -to fia-receiving` station oversaid transmission path -Wliich'produces envelope delay distortions,means at thereceiving'station under control of said pilotfrequency Wavesto produce correetingincrements -ofjenvelope delay of the propermagnitudes and-gatthe-respective pilot frequencies to give-substantiallyflat compensa'- tionof the envelope dela-y versusfrequencycharacteristicv ofy said transmissionlpathi,`and means for.insertingsaid correctingincrernents into the transmission pathtogivesaid substantially flat compensation;y said'last-twomeausr-including a delaydistortionequalizer throughI Which allsaid pilot-."frequency waves; are passed yand whichl equalizer includesa plurality o f parallel circuitsr each comprising a thermistor having aheater,

land lmeans for deriving'ffroin each. pair of adjacent' pilotYfrequency` Wavesa direct current representative of theenvelQpe. delaydistortion over the frequency bandjbetvveen saidl pair of pilotfrequencies for controllingthe. tiemperatureiof Santena.,

31h-iv combinations a ,broad band transmission path for television,signals produced by scanning a field along elementalv lines insuccession,v means for generating oscillations of a. standard fre- 15quency',m"eans' for 'deriving from said standard frequency oscillationsa multiplicity of harmonic frequencyoscillations, means'for selectingfrom said'Y multiplicity vof oscillations a number of` pilot frequency.Wavesi ofjdierent frequencies each one spaced fromian adjacent one bythe line scanning'frequency and located in a vportion of the bandwhichcontains inappreciable television signal energy, means for transmittingsaid pilot frequency Waves to a receiving station over said transmissionpath lWhich `produces attenuation distortions, means at vthe receivingstation under controlof Asaid pilot frequency waves to producecorrectingiincrements of loss .'of the proper magnitude and 'at theproper frequencies to give substantially fiat compensation lof ltheattenuation versusffr'equency characteristic of said transmission path,and-me'ans,for 'inserting said correcting increments intoy thetransmission path togive saidl substantially flat compensation, saidlast two meansincluding an amplifier through which allfsaid pilotfrequency Waves are passed, an attenuation equalizer connected in aVfeedback circuit between the output and input of said amplifier andwhich attenuation equalizer comprises a plurality of parallel circuitstuned to the respective pilot frequencies and each comprising athermistor and a heater, means for deriving from each pair of adjacentpilot frequency Waves a direct current representative of the attenuationdistortionover the frequency band between said pair of pilotfrequencies, and means for utilizingl all 'ofithe direct, currentcontrol signals thereby producedjto control the magnitudes oftheicorrecting increments applied to the transmission path ,toY correctfor said attenuation distortion.Y

4.-, In combination, a broad band transmission path fortelevisionsignals 'produced by scanning a field along elemental lines insuccession, means for transmitting a plurality of pilot frequency Wavesover said path, each of said pilot frequencies being spaced from anadjacent pilot frequency by the line scanning frequency and lcated inraportion Vof the band which contains inappreciablertelevision signalenergy, and means for utilizing each of said pilotfrequency Waves toadjust A*separate networks controlling' the en-v velope delayjandtheattenuation of saidA path about lthat frequency only, said lastmentioned means including switching apparatus for adjusting saidseparatenetworks in rotation.

,5. In combination, a broad band transmission path for televisionsignals produced by scanning a field along elemental-lines insuccession, means for generating oscillations of a standard frequency,means for deriving from said standard frequency oscillations amultiplicity of harmonic frequency oscillations, means for selectingfrom said multiplicity of oscillations a number of Vpilot frequencywaves of different frequencies each one spaced from an adjacent one bythe line scanning frequency and located in a portionr of the band whichcontains inappreciable television signal energy, means for transmittingsaid pilot yfrequency Waves to a receiving station over saidtransmission path which produces envelope delay distortions, means atthe'receiving station under control of said pilot' frequency Waves toproduce correcting increments .ofenvelope delay ofthe proper magnitudesand at the respective pilot frequencies to give substantially flatcompensation of the envelope delay versus frequency characteristicofsaidtransmission path, and means for inserting'said correctinglincrements in to the transmission path to YVgive said substantiallylflatcompensation, said control being afforded .by means includinga pluralityofl parallel circuit branches eachof which passesv a pilot frequency andeach pfvwhich comprises, serially, a demodulator, a low-pass inter, andmeans to ncompare thephase of the signal in each of said plurality ofvparallel fbrancheswith the phase of the signal ineach adjacent branchsoas toyield ,control signals whose magnitude is representative of theenvelope delay distortion over each frequency band between each pairv ofpilot frequencies.

6, In combination, a broad band transmission path for televisionvsignals produced by scanning a field along elemental lines insuccession, means for generating oscillations of a standard frequency,means for deriving from said standard frequency oscillations amultiplicity of harmonic frequency oscillations, means for selectingfrom said multiplicity of oscillations a number of pilot frequency Wavesof` different frequencies each one spaced from an adjacent one by theline scanning frequency Vandrlocated in a portion of the band whichcontains inappreciable television signal energy, means for transmittingsaid pilot frequency Waves to a receiving station over said transmissionpath which produces attenuation distortions, means at the receivingstation under control of said pilot frequency Waves to producecorrectingincrements of loss of the proper magnitudes and at .the respective pilotfrequencies to give substantially fiat compensation'of the attenuationVersus frequency characteristic of said transmission path, and means forinserting said correcting increments into the transmission path to givesaid substantially at compensation, said control being afforded by meansincluding a plurality of parallel circuits each of which passes a pilotfrequency and each of which comprises,

serially, a high frequency attenuator of constant impedance, arectifier, and anvoscillator of variable output controlled by the outputof said rectier. f

7. In combination, a broad band transmissionA path forytelevisionsign'als producedby scanning a neld along elementallines insuccession, means for transmitting aplurality Vof pilot frequencyV Wavesover said path, each of said pilot frequencies being fspacedfrom anadjacent pilotfr'equency .by the. linefscanningVY frequency and lo.-cated in af portion of the band whichcontains inappreciable televisionsignal energy, and means for 'utilizing'each'of said pilot frequencywaves to adjust both the envelope delay and the attenuation of said pathabout th'atfreque'ncyv only.

7 Q REFERENCES Citrine The following references vare of record in thefile of this patent; 'fu-[ PATENTS'

